in california, in 2007, dense fog caused this 100-car pile-up near fresno that killed two. and this is the time of year when fog can move in quickly. >> you get the longer, cooler nights and that basically allowed the temperature to cool all the way down to where that moisture can condense and produce some pretty thick fog. >> reporter: fog is notorious for distorting a driver's perception of speed and distance. experts advise to slow way down. don't forget to use your fog lights, not your high beams. and try to pull way over until the fog clears. overall, traffic fatalities continue to decline year round. over thanksgiving, 610 deaths in 2005 to a projected 451 this year, a 26% drop. thanksgiving is the single busiest travel period of the year for families, with 39 million of us driving over these four days, and sunday will be the single busiest day when so many people start heading back home. tom costello, nbc news, washington. >> once again, here's erica. >>> restaurant chain cracker barrel has been a favorite of american road trippers for decades with its down home sout